The objective of the contract is to provide chemistry support services for the System Toxicity Branch contract toxicology effort and for in-house research projects. Prior to the start of a study or research project, this support consists of the procurement and chemical characterization of test chemicals, analyses to confirm stability of the test chemical during storage, and purity and identity analyses of the test chemical. During the course of a study, support will include analyses performed to confirm that no degradation of the test material has occurred and dose formulation analyses for chemical content. For in-house research projects dose formulations may be prepared and analyzed during the course of the project. Formulations which meet study specifications for chemical concentration will be delivered to the researcher at NIEHS. Many of these analyses will require development of new chemical analysis methodologies for the determination of the test chemical in various matrices, i.e., feed, corn oil, water, or methylcellulose, etc. Post study chemistry support include confirmation of the purity of the test chemical and quantification of the chemical and metabolites present in various biological tissues and fluids. Special analyses, i.e., the determination of vapor or aerosol concentrations in an inhalation exposure system, or identification of impurities in a test chemical, may be required. For options 1 and 2, similar services will be provided for test chemicals which are mixtures. Option 3 provides similar services for AIDS Therapeutics, with the addition of tasks to perform pilot scale toxicokinetic studies in laboratory mice and rats.